This research program is designed to enhance our understanding of the influence of gonadal steroids on social behavior and morphology throughout the lifespan. Current theories of sexual differentiation explain the development of the masculine phenotype as due to organizing actions of androgens secreted by the fetal or neonatal tests. After puberty, further androgenic secretions contribute to activation of the substrates of typically masculine copulatory and aggressive behaviors. We have chosen to study the spotted hyena as a "natural experiment" in masculinization. In this highly social carnivore females are larger than males, more aggressive than males dominant to males and have external genitals that are superficially very similar to those of the male. If contemporary theories are correct, we would expect to find androgens in the female hyena that have produced the suite of conventionally masculine characteristics. During the past study period, we found an androgen (androstenedione), secreted by the ovaries of the female hyena that is present in high levels in the blood during infancy and puberty. This hormone is a natural product of the mammalian ovary and is associated with certain types of infertility in human females (the polycystic ovarian syndrome), as well as correlating with a variety of behavioral characteristics in people. We are studying an unusual animal to reveal general processes. During the period of study proposed here, we intend to examine three life-stages where hormonal influences, or the interaction of hormones with environment, are likely to be of great importance the perinatal period, the time of introduction of infants to the main social group, and the time of sexual maturity. For each of these stages, we will be correlating plasma levels of various hormones with a broad array of behavioral and morphological events (e.g., aggressive interactions alliance formation or genital development). We will also be examining the effects of removal of the ovaries of tests perinatally, and comparing the consequences of gonadectomy at that time with similar procedures carried out in juvenile hyenas during the past grant period. Finally, we will study the result of replacing particular gonadal hormones on behavior and morphology. At a more "molecular" level, we will focus on generation of androgens by the hyena ovary, the possible transformation of these androgens to effective metabolites in target tissues, and the consequences of such androgen production for masculinization of the nervous system.